[0001] The present invention relates to an illumination unit capable of increasing the efficiency
of collecting light emitted from a light source and an image projection apparatus
employing the illumination unit.
[0002] In general, illumination units include a light source emitting light, and an illumination
optical system transmitting light emitted from the light source. Illumination units
are widely used for image projection apparatuses which create an image using an image-forming
device such as a liquid crystal display (LCD) device or a digital light processing
panel (DLP) comprised of a two dimensional array of micromirrors.
[0003] A metal halide lamp or a super-high voltage mercury lamp has been used as a light
source of an illumination unit. Since the life span of these lamps is several thousands
hours at most, the lamps need to be frequently replaced. To solve this problem, research
on the use of a compact light-emitting device such as a light-emitting diode (LED)
having a relatively longer life span has been conducted. Since an LED radiates light
divergently, an illumination unit needs to collect and collimate the light emitted
from the LED such that the light can propagate in one direction.
[0004] The LED emits relatively less light than the metal halide lamp or the super-high
voltage mercury lamp. Accordingly, an array of LED modules must be used as a light
source of image projection apparatuses.
[0005] To collimate light emitted from an LED, the LED modules generally comprise lenses.
The array of LED modules using general lenses has low light efficiency as explained
below.
[0006] The product of the emission area and the solid angle of the light emitted by the
LED is a conserved value called the "etendue". Since the etendue is conserved, the
product of the emission area and the solid angle of the light emitted by the LED should
be equal to the product of the area of the image-forming device and the solid angle
of incidence of the image-forming device. The etendue of the image-forming device
is determined geometrically.
[0007] When an array of LED modules is used, the emission area of the array of LED modules
is larger than the emission area of one LED module because the emission area increases
in proportion to the number of LED modules.
[0008] Here, the solid angle of emission of each LED module is identical to the solid angle
of emission of the array of LED modules, and the area of the image-forming device
is fixed. According to etendue conservation, the solid angle of the incidence of the
image-forming device is greater when the array of LED modules is used than when one
LED module is used. Accordingly, some light exists outside the range of solid angle
where light can be effectively projected by a projection lens and loss of light occurs,
thereby reducing light efficiency. As a result, the luminance of the image-forming
device is limited in spite of a greater number of LEDs.
[0009] According to the present invention there is provided an apparatus and method as set
forth in the appended claims. Preferred features of the invention will be apparent
from the dependent claims, and the description which follows.
[0010] The present invention provides an illumination unit capable of increasing the efficiency
of collecting light emitted from a light source and an image projection apparatus
employing the illumination unit.
[0011] According to an aspect of the present invention, there is provided an illumination
unit comprising: a first reflective surface reflecting light incident thereon; a light-emitting
device generating and emitting illuminating light; and a second reflective surface
reflecting light emitted from the light-emitting device to a light source surface
that includes the light-emitting device.
[0012] The first reflective surface may have a focal point, and the light-emitting device
may be disposed at or around the focal point of the first reflective surface.
[0013] At least one of the first and second reflective surfaces may be selected from the
group consisting of a parabolic reflective surface, a spherical reflective surface,
and an elliptical reflective surface.
[0014] The first reflective surface may be a parabolic reflective surface and the second
reflective surface may be a spherical reflective surface. A spherical center of the
second reflective surface and the focal point of the first reflective surface may
coincide.
[0015] The light-emitting device may be an organic light-emitting diode (OLED) or a light-emitting
diode (LED).
[0016] The illumination unit may comprise a transparent light collector having a light incident
surface, on which the second reflective surface is formed on a certain area of the
light incident surface, and an outer side surface on which the first reflective surface
is formed.
[0017] The light collector may include a light guide portion guiding light reflected by
the first reflective surface.
[0018] The light incident surface of the light collector may be concave, and a predetermined
optical medium or an air layer may exist between the light-emitting device and the
light incident surface of the light collector.
[0019] The light incident surface of the light collector may have a concave dome shape.
[0020] The illumination unit may comprise a two-dimensional array of light collectors and
a plurality of the light-emitting devices respectively corresponding to each of the
light collectors.
[0021] According to another aspect of the present invention, there is provided an image
projection apparatus comprising: at least one illumination unit; an image-forming
device generating an image in response to an input image signal by using light emitted
from the illumination unit; and a projection lens unit enlarging and projecting the
image formed by the image-forming device, wherein the illumination unit comprises:
a first reflective surface reflecting light incident thereon; a light-emitting device
generating and emitting illuminating light; and a second reflective surface reflecting
light emitted from the light-emitting device to a light source surface that includes
the light-emitting device.
[0022] The at least one illumination unit may comprise a plurality of the illumination units
emitting light of different colors, and the image projection apparatus may further
comprise a color synthesis prism synthesizing the light of different colors emitted
from the plurality of illumination units such that the synthesized light of different
colors propagates along one optical path.
[0023] The image projection apparatus may further comprise a light integrator transforming
the light of different colors emitted from the plurality of illumination units into
uniform light.
[0024] The image-forming device may be selected from the group consisting of a transmissive
liquid crystal display device, a reflective liquid crystal display device, and a reflective
image-forming device comprising an array of micromirrors that selectively reflect
the light emitted from the illumination units to form an image.
[0025] The illumination unit may comprise a transparent light collector that includes a
concave dome-shaped light incident surface and a light guide portion guiding light
reflected by the first reflective surface. The second reflective surface may be formed
on a certain area of the light incident surface of the light collector on which light
is incident from the light-emitting device, the first reflective surface may be formed
on an outer side surface of the light collector, and a predetermined optical medium
or an air layer may exist between the light-emitting device and the light incident
surface of the light collector. The at least one illumination unit may comprise a
plurality of illumination units emitting light of different colors. The image projection
apparatus may further comprise: a color synthesis prism synthesizing the light of
different colors emitted from the plurality of illumination units such that the synthesized
light of different colors propagates along one optical path; and a light integrator
transforming the light emitted from the plurality of illumination units into uniform
light. The image-forming device may be selected from the group consisting of a transmissive
liquid crystal display device, a reflective liquid crystal display device, and a reflective
image-forming device comprising an array of micromirrors that selectively reflect
the light emitted from the illumination units to form an image.
[0026] The above and other features and advantages of the present invention will become
more apparent by describing in detail exemplary embodiments thereof with reference
to the attached drawings in which:
Figure 1 is a perspective view of an example illumination unit as found in U.S. Patent Application No. 11/119,918;
Figure 2 is a cross-sectional view taken along line II-II of Figure 1;
Figure 3 is a conceptual view illustrating elements of an illumination unit according
to an embodiment of the present invention;
Figure 4 is a perspective view of the illumination unit of Figure 3;
Figures 5 and 6 are cross-sectional views of illumination units according to other
embodiments of the present invention;
Figure 7 is a perspective view of illumination units according to an embodiment of
the present invention being formed as an array; and
Figures 8 through 10 are top views of image projection apparatuses employing the illumination
unit according to embodiments of the present invention.
[0027] The present invention will now be described more fully with reference to the accompanying
drawings, in which exemplary embodiments of the invention are shown.
[0028] An illumination unit according to the present invention has better light collecting
efficiency than a conventional illumination unit. An example unit is disclosed in
U.S. Patent Application No. 11/119,918, entitled "illumination unit using LED and an image projecting apparatus employing
the same", owned by the applicant of the present invention.
[0030] Referring to Figures 1 and 2, the illumination unit 50 includes a light-emitting
diode (LED) module 10 and a transparent rod 20. The rod 20 includes a parabolic reflective
surface 21, and a light guide portion 24 guiding light reflected by the parabolic
reflective surface 21. A recession 23 is formed in a surface of the rod 20 on which
light is incident. The light guide portion 24 has a rectangular cross-section.
[0031] The LED module 10 includes an LED chip 11 emitting light. The LED module 10 may further
include a dome lens or cap 12. The LED module 10 is disposed at a focal point of the
parabolic reflective surface 21.
[0032] Light emitted from the LED chip 11 and incident on the parabolic reflective surface
21 is reflected by the parabolic reflective surface 21 to be collimated into substantially
parallel light and then is guided by the light guide portion 24 to be emitted out
of the illumination unit.
[0033] In the illumination unit 50, light ℓa incident on the parabolic reflective surface
21, among the light emitted from the LED chip 11, is collimated into substantially
parallel light. The light ℓa is guided to a light exit surface 20' of the rod 20 along
the light guide portion 24. Light ℓb emitted from the LED chip 11 and proceeding outside
the region of the parabolic reflective surface 21 (right side of LED chip 11 in Figure
1) is not collimated into parallel light because it directly enters the light guide
portion 24 without reflecting from the parabolic reflective surface 21. Accordingly,
it is difficult to collect the light ℓb, thereby reducing light collecting efficiency.
[0034] However, an illumination unit according to the present invention can collimate light
proceeding outside of the parabolic reflective surface 21 and propagating directly
into the light guide portion so as to increase light collecting efficiency.
[0035] Figure 3 is a conceptual view illustrating elements of an illumination unit 100 according
to an embodiment of the present invention. Figure 4 is a perspective view of the illumination
unit 100 of Figure 3.
[0036] Referring to Figures 3 and 4, the illumination unit 100 includes a first reflective
surface 120 reflecting light incident thereon, a light-emitting device 130 generating
and emitting light, and a second reflective surface 140 reflecting light Lb. The light
Lb is light emitted by the light-emitting device 130 and propagating outside the region
of the first reflective surface 120. The light Lb is reflected by the second reflective
surface to a light source surface (see 131 in Figures 5 and 6) that includes a light
emission surface 130a of the light-emitting device 130.
[0037] The first reflective surface 120 is curved and has a focal point. The first reflective
surface 120 may be selected from the group consisting of a parabolic reflective surface,
a spherical reflective surface, and an elliptical reflective surface. The first reflective
surface 120 reflects the light from the light-emitting device 130 and collimates the
same into substantially parallel light.
[0038] The light-emitting device 130 may be disposed at or around the focal point of the
first reflective surface 120. The light-emitting device 130 may include a light-emitting
device chip, such as an LED or an organic light-emitting diode (OLED), which is also
called an organic electroluminescent (EL) device.
[0039] The light-emitting device 130 may have reflective properties so that it may reflect
external incident light. Since the light-emitting device chip such as the LED has
a smooth surface, it has a predetermined reflectance. That is, the light-emitting
device 130 may have the basic reflective properties of the light-emitting device chip.
[0040] The light-emitting device 130 may, in addition to such basic reflective properties,
also include a reflective layer (not shown) to further increase reflectance of external
light incident thereon. For example, the reflective layer may be formed between a
substrate of the light-emitting device 130 and a semiconductor layer stacked on the
substrate. In this case, the efficiency of reflecting light by means of the second
reflective surface 140 to the light-emitting device 130, and reflecting light by means
of the light-emitting device 130 to the first reflective surface 120, can be further
increased.
[0041] Since the light-emitting device 130 is not a point light source but an area light
source, some of the light reflected by the second reflective surface 140 may be incident
outside the region of the light-emitting device 130. Accordingly, the light-emitting
device 130 may be installed on a base 135 as shown in Figures 5 and 6, and in this
case, the base 135 may have a reflective surface that reflects the light, which is
reflected by the second reflective surface 140 and incident on the base 135, to the
first reflective surface 120. Referring to Figures 5 and 6, the light source surface
131 may include the light emission surface 130a of the light-emitting device 130 or
the sum region of the light emission surface 130a and the incident light reflecting
region 135a of the base 135.
[0042] The second reflective surface 140 reflects the light Lb propagating outside the region
of the first reflective surface 120 to the light source surface 131 that includes
the light-emitting device 130 so that the light reflected by the light source surface
131 propagates toward the first reflective surface 120. A dotted line in Figure 3
represents a possible path of light proceeding outside the region of the first reflective
surface 120 such that the output light lacks collimation as parallel light when the
second reflective surface 140 is not present.
[0043] The second reflective surface 140 may be selected from the group consisting of a
parabolic reflective surface, a spherical reflective surface, and an elliptical reflective
surface, like the first reflective surface 120.
[0044] A considerable amount of the light reflected by the second reflective surface 140
to be directed to the light-emitting device 130 and then, to the first reflective
surface 120 is collimated into parallel light by the first reflective surface 120.
[0045] Accordingly, since the illumination unit 100 according to the present embodiment
includes the second reflective surface 140 to reflect and feed the light Lb propagating
in the region beyond the first reflective surface 120 back to the light-emitting device
130, the illumination unit 100 has higher light collecting efficiency than the illumination
unit disclosed in
U.S. Patent Application No. 11/119, 918.
[0046] The propagation of light with respect to the first and second reflective surfaces
120 and 140 according to various embodiments of the present invention will now be
explained from the point of view of the collimation of light emitted from the illumination
unit 100 into substantially parallel light rays.
[0047] For example, the first reflective surface 120 may be a parabolic reflective surface
and the second reflective surface 140 may be a spherical reflective surface. The light-emitting
device 130 may be disposed at or around a focal point of the first reflective surface
120, or at a spherical center of the second reflective surface 140. The focal point
of the first reflective surface 120 and the spherical center of the second reflective
surface 140 may be identical to each other, in which case the light-emitting device
130 may be disposed at the focal point of the first reflective surface 120 and at
the spherical center of the second reflective surface 140.
[0048] In this case, light La emitted from the light-emitting device 130, which is disposed
at the focal point of the first reflective surface 120, and propagating to the parabolic
first reflective surface 120 is reflected and collimated by the first reflective surface
120 into substantially parallel light. The light Lb emitted from the light-emitting
device 130 and propagating to the spherical second reflective surface 140 is reflected
by the second reflective surface 140 and focused on the light-emitting device 130.
The focused light is reflected by the light-emitting device 130 to propagate divergently
to the first reflective surface 120 and then is collimated by the first reflective
surface 120 into substantially parallel light to travel in the same direction as the
light La that is emitted from the light-emitting device 130 and directly incident
on the first reflective surface 120.
[0049] When the first reflective surface 120 is a parabolic reflective surface and the second
reflective surface 140 is a spherical reflective surface, in this way, diverging light
emitted from the light-emitting device 130 can be collimated into substantially parallel
light to maximize the amount of light effectively emitted from the illumination unit
100.
[0050] Even when the first reflective surface 120 is a parabolic reflective surface and
the light-emitting device 130 is disposed at the focal point of the first reflective
surface 120, the light emitted from the light-emitting device 130 is collimated by
the first reflective surface 120 into substantially parallel light, but not perfectly
parallel light, because the light-emitting device 130 is not a point light source
but an area light source. Since the light-emitting device 130 is an area light source,
despite the spherical second reflective surface 140, not all the light reflected by
the second reflective surface 140 is focused on one point of the light-emitting device
130. Still, a high percentage of the light is focused on the light-emitting device
130.
[0051] In the illumination unit 100, the light generated and emitted by the light-emitting
device 130 is collimated into substantially parallel light. Here, the term "substantially
parallel light" includes nearly parallel light having a divergent angle or a convergent
angle within a range where the light can be collected by subsequent optical components.
[0052] Various embodiments are possible within the combination wherein each of the first
reflective surface 120 and the second reflective surface 140 may be selected from
one of a parabolic reflective surface, a spherical reflective surface, or an elliptical
reflective surface.
[0053] For example, the first reflective surface 120 may be a spherical reflective surface
to reflect divergent light emitted from the light-emitting device 130 disposed at
or around a focal point of the first reflective surface 120 and collimate the reflected
light into substantially parallel light.
[0054] The first reflective surface 120 may be an elliptical reflective surface to reflect
divergent light emitted from the light-emitting device 130 disposed at or around a
focal point of the first reflective surface 120 and collimate the reflected light
into substantially parallel light.
[0055] As is well known, an ellipse has two focal points. Accordingly, divergent light emitted
from the light-emitting device 130 disposed at one focal point incident on the elliptical
reflective surface is reflected by the elliptical reflective surface to be focused
on the other focal point of the elliptical reflective surface.
[0056] Accordingly, when the first reflective surface 120 is an elliptical reflective surface
having two focal points distant from each other, light reflected by the first reflective
surface 120 can be collimated into almost parallel light. Thus, when the first reflective
surface 120 is an elliptical reflective surface close to a parabolic reflective surface,
light reflected by the first reflective surface 120 can be collimated into substantially
parallel light. Also, when the first reflective surface 120 is an elliptical reflective
surface close to a spherical reflective surface, light reflected by the first reflective
surface 120 can be collimated into substantially parallel light. The spherical reflective
surface is an elliptical reflective surface whose two focal points coincide with each
other.
[0057] Accordingly, even when the first reflective surface 120 is an elliptical reflective
surface, light incident from the light-emitting device 130 can be collimated into
substantially parallel light. The ratio of substantially parallel light which can
be collected changes with the ellipticity of the first reflective surface 120.
[0058] The second reflective surface 140 may be a parabolic reflective surface, an elliptical
reflective surface, or most preferably, a spherical reflective surface. Although the
amount of light reflected by the parabolic or elliptical second reflective surface
140 to the light source surface 131 including the light-emitting device 130 and directed
to and reflected by the first reflective surface 120 to be collimated into substantially
parallel light is less than the amount of collimated substantially parallel light
obtained through the usage of the spherical second reflective surface 140, the overall
light collecting efficiency can be greatly increased with the use of the second reflective
surface 140 compared to the case when the second reflective surface 140 is not used.
[0059] In describing the reflective surfaces 120 and 140, the term "parabolic surface" does
not denote a parabolic surface strictly having a conic coefficient K of -1. The term
"parabolic surface" used herein denotes an aspherical surface having a conic coefficient
K between -0.4 and - 2.5, preferably, between -0.7 and -1.6. The conic coefficient
K for the parabolic surface may be appropriately selected within the above range so
as to collimate light emitted from the light-emitting device 130 within a range of
radiation angles which result in effective illumination of an object.
[0060] The illumination unit 100 constructed as above permits the divergent light La emitted
from the light-emitting device 130 and propagating to the first reflective surface
120 to be reflected and collimated by the first reflective surface 120. The reflected
light is formed as parallel light according to the structure of the first reflective
surface 120.
[0061] Since the light Lb emitted from the light-emitting device 130 and not propagating
toward the first reflective surface 120 cannot be collimated in a conventional illumination
unit, light collecting efficiency is deteriorated. To solve this problem, the illumination
unit 100 of the present embodiment includes the second reflective surface 140 which
reflects the light Lb to the light source surface 131 so that the light reflected
by the light source surface 131 can be guided toward the first reflective surface
120, thereby being formed as parallel light by the first reflective surface 120.
[0062] The illumination unit 100 can increase light collecting efficiency by reflecting
at least some of the light Lb, which is not produced as parallel light in a conventional
illumination unit, by means of the second reflective surface 140 back to the light
source surface 131.
[0063] Consequently, the illumination unit 100 according to the present embodiment can achieve
higher light collecting efficiency than the illumination unit 100 disclosed in
U.S. Patent Application No. 11/119,918 filed by the applicant of the present invention.
[0064] Figures 5 and 6 are cross-sectional views of illumination units 100 according to
other embodiments.
[0065] Referring to Figures 5 and 6, the illumination unit 100 includes a transparent light
collector 110 having a light incident surface 125 on which light is incident from
the light-emitting device 130. The second reflective surface 140 may be formed on
a certain area of the light incident surface 125 of the light collector 110, and the
first reflective surface 120 may be formed on an outer side surface of the light collector
110.
[0066] The light incident surface 125 is concave. The light incident surface 125 may have
a concave dome shape. In this case, the light-emitting device 130 can be disposed
at a focal point of the first reflective surface 120, and the second reflective surface
140 can be formed with a dome shape on a certain area of the light incident surface
125. The light-emitting device 130 is installed on the base 135, and the base 135
is coupled to the light collector 110. The base 135 may have a reflective surface
that can reflect light reflected by the second reflective surface 140 to the first
reflective surface 120 as described above. The surface of the base 135 may be coated
to reflect light.
[0067] In the illumination unit 100 according to the present embodiment, a predetermined
optical medium 137 having a refractive index higher than air may be disposed between
the light-emitting device 130 and the light incident surface 125 as shown in Figure
5. Alternatively, an air layer 137' may be filled between the light-emitting device
130 and the light incident surface 125 as shown in Figure 6.
[0068] The optical medium 137 may be a dome lens or cap of the light-emitting device 130.
The optical medium 137 may be a medium additionally filled between the light-emitting
device 130 and the light incident surface 125. When the light-emitting device 130
includes a dome lens or cap and the optical medium 137 exists, the refractive index
of the optical medium 137 may be equal to the refractive index of the transparent
light collector 110, or may be between the refractive index of the dome lens or cap
and the refractive index of the transparent light collector 110.
[0069] In the illumination unit 100 of the present embodiment, the light collector 110 may
further include a light guide portion 150 extending from the transparent body of the
light collector 110. The light guide portion 150 guides light reflected by the first
reflective surface 120 and collimated into parallel light. The light guide portion
150 may have a rectangular cross-section.
[0070] The light guide portion 150 may be formed to be stepped to decrease the area of the
cross-section of the light guide portion 150 with respect to the portion of the light
collector 110 where the light-emitting device 130 is coupled. That is, the light-emitting
device 130 may protrude downward from the light collector 110 such that the light-emitting
device 130 is lowered below the light guide portion 150. There exists the area which
blocks light propagating to the light guide portion 150, i.e., the second reflective
surface 140. Thus, to focus light at a center of a light exit surface of the light
guide portion 152, not at an upper portion of the light exit surface of the light
guide portion 152, the light guide portion 150 should be stepped.
[0071] The amount by which the light guide portion 150 is stepped with respect to the portion
of the light collector 110 where the light-emitting device 130 is coupled can be appropriately
determined within a range allowing light to be uniformly emitted from the entire light
exit surface of the light guide portion 150 considering the size of the light blocking
area of the second reflective surface 140.
[0072] When the light guide portion 150 is stepped above the portion of the light collector
110 where the light-emitting device 130 is coupled, modules of the light-emitting
device 130 and the light collector 110 can be more easily arrayed, and a more uniform
light distribution can be achieved on an exit surface of the array of the light collectors.
[0073] Since an LED emits less light than a conventional metal halide lamp or a super-high
voltage mercury lamp, the light-emitting device 130 may include an array of LEDs.
[0074] Thus, illumination unit 100 according to the present invention may be formed as an
array, as shown in Figure 7. Figure 7 is a perspective view of illumination units
100 according to an embodiment of the present invention being formed as an array.
Referring to Figure 7, the illumination unit 100 includes a two-dimensional array
of modules of light-emitting devices 130 and light collectors 110 in which a plurality
of light collectors 110 are arranged in two dimensions and a plurality of light-emitting
devices 130 respectively correspond to the light collectors 110. The light-emitting
device 130 and the base 135 configure a light-emitting module.
[0075] Since the illumination unit 100 can collimate most light emitted from the light-emitting
device 130 into substantially parallel light by recycling at least some light emitted
from the light-emitting device 130 which may be lost, by means of the second reflective
surface 140, the illumination unit 100 can have high light collecting efficiency and
can be used as an illumination source for various systems. For example, the illumination
unit 100 may be used as an illumination source for image projection apparatuses or
as a headlight for vehicles.
[0076] An image projection apparatus using the illumination unit 100 as an illuminating
light source according to various embodiments of the present invention will now be
explained.
[0077] Figure 8 is a top view of an image projection apparatus employing the illumination
unit 100 according to an embodiment of the present invention.
[0078] Referring to Figure 8, the image projection apparatus includes first through third
illumination units 100R, 100G, and 100B, an image-forming device forming an image
in response to an image signal using light incident from the first through third illumination
units 100R, 100G, and 100B, and a projection lens unit 250 enlarging and projecting
the image formed by the image-forming device onto a screen s.
[0079] The first through third illumination units 100R, 100G, and 100B may each be an illumination
unit 100 of an array form as shown in Figure 7. That is, each of the first through
third illumination units 100R, 100G, and 100B may include a two dimensional array
of light collectors 110 and light-emitting devices 130 which correspond to each of
the light collectors 110.
[0080] Since the light-emitting device such as an LED emits less light than a metal halide
lamp or a super-high voltage mercury lamp, an array of light-emitting devices may
be used.
[0081] The first through third illumination units 100R, 100G, and 100B may emit red light,
green light, and blue light, respectively.
[0082] When the first through third illumination units 100R, 100G, and 100B emit different
colors of light, a color synthesis prism 201, for example, an X-cube prism, may be
further used to synthesize the different colors of light emitted from the first through
third illumination units 100R, 100G, and 100B such that the synthesized colors of
light can propagate along a single optical path. The image projection apparatus according
to the present invention may include a single illumination unit emitting white light,
and, in this case, the color synthesis prism 201 is not necessary.
[0083] The image projection apparatus according to the present invention may further include
a light integrator that transforms incident light into uniform light. The light integrator
integrates light incident along the same optical path after emission from the first
through third illumination units 100R, 100G, and 100B and being synthesized such that
the light is uniform.
[0084] The light integrator may be a rectangular parallelepiped light tunnel 205 as shown
in Figure 8. The rectangular parallelepiped light tunnel 205 may be hollow or an optical
medium block. A pair of fly-eye lenses (see 320 in Figure 9) may be used as the light
integrator, instead of the light tunnel 205.
[0085] The first through third illumination units 100R, 100G, and 100B have a light exit
surface, and the light tunnel 205 has a light incident surface. The light exit surface
of the first through third illumination units 100R, 100G, and 100B and the light incident
surface of the light tunnel 205 may have similar forms. The light exit surface of
the first through third illumination units 100R, 100G, and 100B and the light incident
surface of the light tunnel 205 may have a rectangular shape having the same aspect
ratio as the image forming device 200.
[0086] To this end, the light guide portions 150 of the light collectors 110 in each of
the first through third illumination units 100R, 100G, and 100B are arranged in a
two dimensional array to form a rectangular shape having the same aspect ratio as
the light tunnel 205.
[0087] The image projection apparatus of the present invention may further include a condenser
lens 203 along an optical path between the color synthesis prism 201 and the light
tunnel 205 to condense light emitted from first through third light source units 10a,
10b, and 10c and synthesized by the color synthesis prism 201 to direct the light
along a single optical path such that the condensed light having reduced beam size
is incident on the light tunnel 205.
[0088] In the present embodiment, the image-forming device is a reflective image-forming
device, which controls incident uniform light for each pixel to produce an image.
[0089] In Figure 8, the reflective image-forming device is a digital light processing (DLP)
panel 200 or a digital micromirror device (DMD) with an array of micromirrors. The
reflective image-forming device may be a reflective liquid crystal display (LCD).
Alternatively, the image-forming device may be a transmissive LCD.
[0090] The DLP panel 200 includes a two-dimensional array of independently driven micromirrors,
and creates an image by changing the angle of reflection light for each pixel based
on an input image signal.
[0091] When the image-forming device is a reflective image-forming device, an optical path
changer may be disposed between the light tunnel 205 and the reflective image-forming
device to change the propagation path of incident light by directing light incident
from the light tunnel 205 to the reflective image-forming device and light reflected
by the reflective image-forming device to the projection lens unit 250. When the reflective
image-forming device is the DLP panel 200, a total internal reflection (TIR) prism
70 may be used as the optical path changer as shown in Figure 8.
[0092] A relay lens 207 may be disposed between the light integrator and the optical path
changer, that is, between the light tunnel 205 and the TIR prism 70, to scale up or
down light emitted from the light integrator according to the effective area of the
image-forming device.
[0093] In the image projection apparatus according to the present embodiment, light containing
image information formed on the DLP panel 200 is transmitted through the TIR prism
70 and directed to the projection lens unit 250, and the projection lens unit 250
enlarges and projects the image formed on the DLP panel 200 onto the screen s.
[0094] Figure 9 is a top view of an image projection apparatus employing the illumination
unit 100 according to another embodiment of the present invention. In the drawings,
the same elements are designated by the same reference numerals, and a detailed explanation
thereof will not be repeated.
[0095] Referring to Figure 9, the image projection apparatus according to another embodiment
of the present invention includes a reflective LCD 300 as an image-forming device,
unlike the image projection apparatus illustrated in Figure 8. The image projection
apparatus according to the present embodiment may include a pair of fly-eye lenses
320 comprised of an array of a plurality of lens cells having the shape of a convex
lens or cylindrical lens cells as the light integrator. Alternatively, the light tunnel
205 (see Figure 8) may be used as the light integrator, instead of the fly-eye lenses
320.
[0096] The reflective LCD 300 selectively reflects incident uniform illuminating light for
each pixel to produce an image. The reflective LCD 300 forms an image by changing
the polarization state of incident light for each pixel based on an image signal to
turn on or off light to be reflected.
[0097] When the image-forming device is the reflective LCD 300, a polarization beam splitter
310 may be used as an optical path changer to change the propagation path of incident
light. The polarization beam splitter 310 changes the propagation path of incident
light by directing light with a polarization incident from the first through third
illumination units 100R, 100G, and 100B to the reflective LCD 300 and light with another
polarization reflected by the reflective LCD 300 to the projection lens unit 250.
[0098] To increase light efficiency, a polarization converting unit 330 may be disposed
along an optical path between the fly-eye lenses 320 and the polarization beam splitter
310 so that light emitted from the first through third illumination units 100R, 100G,
and 100B and incident on the polarization beam splitter 310 has a single polarization.
The polarization converting unit 330 converts most non-polarized light incident thereon
into light with a specific polarization by separating light according to polarizations
using a plurality of small polarization beam splitters and disposing a half-wave plate
only in an optical path of light with a predetermined polarization. The polarization
converting unit is well known in the art.
[0099] Figure 10 is a top view of an image projection apparatus employing the illumination
unit 100 according to still another embodiment of the present invention.
[0100] Referring to Figure 10, the image projection apparatus according to still another
embodiment of the present invention includes a transmissive LCD 380 as an image-forming
device, unlike the image projection apparatus illustrated in Figure 9. When the transmissive
LCD 380 is used as the image-forming device, the polarization beam splitter 310 (see
Figure 9) functioning as the optical path changer is not necessary.
[0101] The transmissive LCD 380 forms an image by changing the polarization state of incident
uniform light for each pixel based on an image signal to turn on or off light to be
transmitted.
[0102] The illumination unit 100 can be applied to various image projection apparatuses
as described above.
[0103] As described above, the illumination unit and the image projection apparatus employing
the illumination unit can collimate most light emitted form the light-emitting device
into substantially parallel light and thus ensure high light collecting efficiency
without using lenses by using the second reflective surface that reflects light emitted
from the light-emitting device and propagating outside the region of the first reflective
surface back to the first reflective surface via the light-emitting device.
[0104] Although a few preferred embodiments have been shown and described, it will be appreciated
by those skilled in the art that various changes and modifications might be made without
departing from the scope of the invention, as defined in the appended claims.
[0105] Attention is directed to all papers and documents which are filed concurrently with
or previous to this specification in connection with this application and which are
open to public inspection with this specification, and the contents of all such papers
and documents are incorporated herein by reference.
[0106] All of the features disclosed in this specification (including any accompanying claims,
abstract and drawings), and/or all of the steps of any method or process so disclosed,
may be combined in any combination, except combinations where at least some of such
features and/or steps are mutually exclusive.
[0107] Each feature disclosed in this specification (including any accompanying claims,
abstract and drawings) may be replaced by alternative features serving the same, equivalent
or similar purpose, unless expressly stated otherwise. Thus, unless expressly stated
otherwise, each feature disclosed is one example only of a generic series of equivalent
or similar features.
[0108] The invention is not restricted to the details of the foregoing embodiment(s). The
invention extends to any novel one, or any novel combination, of the features disclosed
in this specification (including any accompanying claims, abstract and drawings),
or to any novel one, or any novel combination, of the steps of any method or process
so disclosed.
1. An illumination unit (100) comprising:
a first reflective surface (120) for reflecting light incident thereon;
a light-emitting device (130) for generating and emitting illuminating light; and
a second reflective surface (140) for reflecting light emitted from the light-emitting
device (130) toward a light source surface (131) that includes the light-emitting
device (130).
2. The illumination unit (100) of claim 1, wherein the second reflective surface (140)
reflects light traveling outside a region of the first reflective surface (120) back
toward the light source surface (131).
3. The illumination unit (100) of claim 1 or 2, wherein the light reflected by the second
reflective surface (140) is directed to the light source surface (131) and then to
the first reflective surface (120).
4. The illumination unit (100) of claim 1, 2 or 3, wherein the first reflective surface
(120) has a focal point, and the light-emitting device (130) is disposed at or around
the focal point of the first reflective surface (120).
5. The illumination unit (100) of claim 4, wherein at least one of the first and second
reflective surfaces (120, 140) is selected from the group consisting of a parabolic
reflective surface, a spherical reflective surface, and an elliptical reflective surface.
6. The illumination unit (100) of claim 4, wherein the first reflective surface (120)
is a parabolic reflective surface and the second reflective surface (140) is a spherical
reflective surface.
7. The illumination unit (100) of claim 6, wherein a spherical center of the second reflective
surface (140) and the focal point of the first reflective surface (120) coincide.
8. The illumination unit (100) of any preceding claim, wherein the light-emitting device
(130) is an organic light-emitting diode (OLED) or a light-emitting diode (LED) or
arrays thereof.
9. The illumination unit (100) of any of claims 1 to 8, comprising a transparent light
collector (110) having a light incident surface (125), wherein the second reflective
surface (140) is formed on a certain area of the light incident surface (125), and
an outer side surface on which the first reflective surface (120) is formed.
10. The illumination unit (100) of claim 9, wherein the light collector (110) includes
a light guide portion (150) for guiding light reflected by the first reflective surface
(120).
11. The illumination unit (100) of claim 9 or 10, wherein the light incident surface (125)
of the light collector (110) is concave, and a predetermined optical medium (137)
or an air layer (137') is provided between the light-emitting device (130) and the
light incident surface (125) of the light collector (110).
12. The illumination unit (100) of claim 11, wherein the light incident surface (125)
of the light collector (110) has a concave dome shape.
13. The illumination unit (100) of claim 10, comprising a two-dimensional array of the
light collectors (110) and a plurality of the light-emitting devices (130) respectively
corresponding to each of the light collectors (110).
14. An image projection apparatus comprising:
at least one illumination unit (100) as set forth in any of claims 1 to 13;
an image-forming device (200) for generating an image in response to an input image
signal using light emitted from the illumination unit (100); and
a projection lens unit (250) for enlarging and projecting the image formed by the
image-forming device (200).
15. The image projection apparatus of claim 14, wherein the at least one illumination
unit (100) comprises a plurality of the illumination units (100R, 100G, 100B) for
emitting light of different colors, the image projection apparatus further comprising
a color synthesis prism (201) for synthesizing the light of different colors emitted
from the plurality of illumination units (100R, 100G, 100B) such that the synthesized
light of different colors propagates along one optical path.
16. The image projection apparatus of claim 15, further comprising a light integrator
(205) for transforming the light of different colors emitted from the plurality of
illumination units (100R, 100G, 100B) into uniform light.
17. The image projection apparatus of claim 14, 15 or 16, wherein the image-forming device
(200) is selected from the group consisting of a transmissive liquid crystal display
device, a reflective liquid crystal display device, and a reflective image-forming
device (200) comprising an array of micromirrors that selectively reflect the light
emitted from the illumination units to form an image.
18. The image projection apparatus of claim 14, wherein the illumination unit (100) comprises
a transparent light collector (110) that includes a concave dome-shaped light incident
surface (125) and a light guide portion (150) guiding light reflected by the first
reflective surface (120),
wherein the second reflective surface (140) is formed on a certain area of the light
incident surface (125) of the light collector (110) on which light is incident from
the light-emitting device (130), the first reflective surface (120) is formed on an
outer side surface of the light collector (110), and a predetermined optical medium
(137) or an air layer (137') exists between the light-emitting device (130) and the
light incident surface (125) of the light collector (110),
wherein the at least one illumination unit (100) comprises a plurality of illumination
units (100R, 100G, 100B) emitting light of different colors,
the image projection apparatus further comprising:
a color synthesis prism (201) synthesizing the light emitted from the plurality of
illumination units (100R, 100G, 100B) such that the synthesized light of different
colors propagates along one optical path; and
a light integrator (205) transforming the light emitted from the plurality of illumination
units (100R, 100G, 100B) into uniform light,
wherein the image-forming device (200) is selected from the group consisting of a
transmissive liquid crystal display device, a reflective liquid crystal display device,
and a reflective image-forming device (200) comprising an array of micromirrors that
selectively reflect the light emitted from the illumination units to form an image.
19. The image projection apparatus of claim 18, wherein each of the illumination units
includes a two-dimensional array of the light collectors (110) and a plurality of
the light-emitting devices (130) respectively corresponding to the light collectors
(110).